There are numerous structures known as smart structures which contain electronic components that produce an electrical signal when stimulated. These components could be strain gauges, switches, thermocouples or other electronic devices. Conventionally, these components have been attached to an existing structure rather than being fabricated in place at the same time the surrounding structure is made.
Electronic packages are another structure in which electronic components are surrounded by another material. Electronic components ranging from an individual integrated circuit chip to an array of interconnected chips have been packaged in protective containers. These containers are often designed to provide more than weather proofing. They may include shielding from electro magnetic interferences, thermal cooling and shock absorption. Blocks of styrofoam having cavities into which electronic devices and components are placed are commonly used today. Plastic encapsulation is another means for protectively packaging electronic components.
Many electronic packages are designed so as never to be opened. In these packages conductors are provided to interconnect the electronic components. An external connector in the package allows one to utilize the package components. Sometimes sensors have been provided in these packages.
Traditionally, the art has first formed the electronic components, interconnected them on a board and placed this system in a housing which may then be filled with a nonconductive material. Each of these steps is performed independently and final assembly involves mechanical connections between boards and the system housing. This manufacturing approach limits packaging density, performance, reliability and shape and requires several assembly steps.
At one time circuit boards were made by hand wiring components mounted on a board. In addition to being a slow process, this manufacturing approach had performance, reliability, shape and size limitations. Many of these problems were overcome by printing processes for circuit boards. In this process one or more layers of material were deposited on a substrate and then circuitry and other features were formed by etching. This printing process, however, is useful for only a limited number of materials and cannot be used for forming several different materials in a single layer.
The prior art contains several other methods for creating objects by the incremental material build up of thin layers. However, such techniques have been used primarily for products other than electrical components. These processes include lamination, selective laser sintering, ballistic particle manufacturing, three-dimensional printing, stereolithography and near net thermal spraying. Lamination involves the simple process of cutting layers of a selected material and then bonding those layers together. The layers may be pre-cut to shapes corresponding to a cross section through the article to be created. Alternatively, standard shapes of material can be stacked and bonded together. Then, the assembled structure is cut or machined to produce the desired shape. In U.S. Pat. No. 4,752,352, Michael Feygin proposes a computer controlled method and apparatus for forming a laminated object. He provides a supply station, a work station for forming a material into a plurality of layers for lamination, an assembly station for stacking the layers in sequence into a three-dimensional object, a station for bonding the laminations to complete the formation of the three-dimensional object and a control station. In his patent, Mr. Feygin discloses a method in which the laminations are cut from a roll of material lifted, stacked and bonded under the direction of a computerized controller. The layers are bonded together by adhesive or brazing. This and other lamination techniques have significant disadvantages. The bond between layers is critical and limits the strength of the object. Moreover, lamination is suitable for only those materials which can be formed into thin layers which can be bonded together.
In laser sintering, a laser is used to cure a starting material into a certain configuration according to the manner in which the laser is applied to that material. Stereolithography is a more recent yet similar process which creates plastic prototype models directly from a vat of liquid photocurable polymer by selectively solidifying it with a scanning laser beam. An example of this method is described in European Patent 322 257. Both of these methods require a substantial amount of curable raw material. In both cases the laser must be carefully controlled to achieve the desired shape. In some applications, the laser typically does not fully cure each cross section. Rather, the laser cures the boundary of a section and then cures an internal structure or honeycomb that traps the uncured fluid. Thereafter, the article must be subjected to final curing under separate ultraviolet lights or heat treatment. Additional post processing, such as careful sanding and grinding, is required for making smooth, accurate surfaces.
In ballistic powder metallurgy beams of particles are directed to the coordinates of a three-dimensional object in a three-dimensional coordinate system. A physical origination seed to which the particulate matter is attracted is required. The process may use a beam of particles directed to the origination seed which builds the particles upward from that seed. Alternatively, one can use an energy beam which attracts the particulate matter already in the environment to the seed or another coordinate. Such a system is disclosed by William E. Masters in U.S. Pat. No. 4,665,492. This method cannot be used to make objects having undercuts therein without creating support structures at the same time. Normally, the support structures are created with the particle beam during the creation of the object. Such support structures must be removed by cutting, grinding or machining. Furthermore, the art has only been able to reliably deposit wax with this method. The usefulness of this method for other materials has not and possibly cannot be established.
Three-dimensional printing is another technique similar to ballistic powder metallurgy. One variation of this technique creates layers of particles to produce a three-dimensional image in much the same manner that an ink jet printer produces two-dimensional images. The technique relies upon thermal shock or drop on demand material delivery techniques. A thermal shock technique forms a particle by vaporizing a small area of the fluid directly behind the nozzle. The drop on demand nozzle includes a piezo electric element to constrict the cavity thereby forcing a drop past the nozzle plate. In both instances the material is directed to a work surface in a manner to build up the article. This technique can only be used for certain kinds of materials.
In another variation of three-dimensional printing a series of two dimensional layers are created by adding a layer of powder on top of a work surface The powdered layer is selectively joined where the part is be formed by ink jet printing of a binder material The work surface is then lowered and another layer of powder is spread out and selectively joined. The layering process is repeated until the part is completely printed. Following a heat treatment the unbonded powder is removed leaving the fabricated part. Although this technique has been proposed for metal, ceramic and plastic materials, it is limited to those materials to which a reliable binder can be applied.
The art has attempted to make objects by spraying layers of metal on a substrate. Problems have occurred in that the layers have tended to camber and possibly to peel apart from the substrate. Therefore, one must have a release agent or compatible substrate.
None of the just described incremental material layer build up techniques have been successfully used to make packaged electronic components or smart structures.
There is a need for a method to manufacture electronic packaging systems and smart structures by incremental build-up of material. The method and apparatus should be capable of producing articles having undercuts and irregular shapes.